Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 121720 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1220 PM EST Thu Jan 12 2017 .SYNOPSIS... A warm front across northern Virginia into the Maryland Panhandle will continue to lift north of the region today. A new cold front will approach the region from the west late tonight into early Friday, then stall across northern North Carolina Saturday before return north as a warm front late Saturday. This later front will then oscillate north and south across the region into early next week keeping an unsettled and wet weather pattern in place. && .NEAR TERM /THROUGH TONIGHT/...
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As of 400 AM EST Thursday... A cold front will approach from the west tonight, then drift south into the region Friday stalling across northern NC Friday night, then is destined to oscillate about the region through the weekend keeping an unsettled, wet pattern in place. More on that scenario in the Short Term section below. The rest of today should be a relatively dry and quiet day weather wise across the region. The region is essentially in a warm sector, unlike any recent weather patterns. Although there will be lots of cloud cover, strong southwest flow aloft (a 60kt southwest jet at 850mb just to our west/north), the presence of the warm sector, and 850mb temperatures in the +10C to +12C range will yield a very warm day, in fact about 20 degrees above normal. Temperatures today should have no problem surging into the 50s to lower 60s, especially given that some areas are already in the 60s early this morning across the west. The coldest locations should continue to be the eastern areas where residual snow cover will temper warming, although much of the snow cover disappeared Wednesday with the rain and temperatures above freezing all day, so the effect of the snow cover may be more limited than current thinking. MOS guidance from the various models appeared too cold and was likely reflecting the residual snow cover. Ended up using a blend of several models, but even then had to raise readings a few degrees across the board. Tonight will remain mild with the area remaining in the warm sector ahead of the next front. Low temperature will only be in the 40s and 50s. Contrast these readings with the below zero and single digit temperatures that we in place just a few days ago. Expecting very little precipitation today or tonight, although some scattered light rain will drift into the far western/southwestern areas late tonight/early Friday in advance of the next front.
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&& .SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/... AS OF 430 AM EST Thursday... We will be in the southern stream of a split flow regime with a closed low near the Baja peninsula and some flat ridging over the southeastern US, through the ridge will amplify a bit as the low starts to open and ejects off to the northeast. This pattern will produce wind flow generally parallel to a baroclinic zone to our west and limit any eastward progress. Strong surface high pressure moving through the Great Lakes will wedge down east of the Appalachians and push backdoor cold fronts through the region with cool and damp conditions and below normal temperatures through the weekend. With a typical wedge configuration expected, locations along the western periphery from the Mountain Empire of VA into the northwest mountains of NC will see milder conditions. The first wedge will start to push in during the afternoon on Friday and will bring an abrupt end to our well above normal temperatures. Isentropic lift over the top of the wedge will bring increasing chances for precipitation into Friday night, and as the cold wedge continues to build some freezing rain and possibly sleet is expected to develop from Greenbrier WV through the Alleghany Highlands and down the Blue Ridge a bit. While the depth of below freezing air in the wedge will be shallow, it will be quite slow to moderate and the freezing rain will gradually transition to plain rain through Saturday. Any glaze of ice is expected to be less than one tenth inch and may trigger an advisory if later model runs remain consistent. A wave will run along the baroclinic zone and may disrupt the wedge a bit on Saturday night, but another strong high will wedge in for Sunday and Sunday night. At this time it looks like just a chance of cold rain for everyone but temperatures trends will be monitored closely. && .LONG TERM /MONDAY THROUGH WEDNESDAY/... .AS OF 334 PM EST Wednesday... Amplified southern stream to take shape into next week with 2-3 systems moving from the desert SW northward/northeastward to the upper MS Valley. Will still be on the cloudier side at times, but at the moment Monday looks like the driest day with highs in the 50s. Will see frontal boundary approach midweek with southwest flow increasing aloft keeping temperatures well above normal. Will see some showers scattered around Tuesday with better chance Wed-Wed night as the front tracks west of the Appalachians. && .AVIATION /17Z THURSDAY THROUGH MONDAY/...
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As of 1217 PM EST Thursday... Warm front has lifted well north of the CWA into PA, leaving the area in a warm sector. Current warm sector air mass will remain in place until a backdoor front arrives late Friday into Saturday. The warm sector air mass is largely void of the lower ceilings at this time. Winds will increase this afternoon with a strong 850mb jet traversing the region. Overnight, as winds veer more to the WSW across eastern WV, expect low clouds to potentially develop with ceilings dropping into the MVFR range at KLWB, KBLF, and possibly KBCB as well. Still expect VFR cigs further east across the Piedmont. Medium to high confidence in cigs throughout the TAF valid period. Medium to high confidence in vsbys throughout the TAF valid period. Medium to high confidence in wind dir/spd throughout the TAF valid period. Extended Aviation Discussion... Should see mainly sub-VFR to start Friday as a backdoor frontal system works its way south into the region by Friday evening. However locations across the north could see enough drying behind the front to briefly return to VFR late Friday as the axis of moisture drifts to the south. Locations across the southern part of the CWA may also remain VFR through the period. Low level moisture will then arc back north Friday night into Saturday, maintaining the threat for additional sub- VFR in low cigs/fog, along with light rain and/or drizzle, including possible patchy freezing rain across the northern Blue Ridge. Unsettled weather will continue into Sunday with some slow improvement in conditions as high pressure weakens to the north leaving the residual weak front near the area. However given uncertainty appears mainly MVFR to prevail under passing showers as the boundary likely oscillates across parts of the region. Southerly flow aloft will develop Monday ahead of a frontal system in the Central Plains with continued MVFR as the low level wedge redevelops while helping keep low clouds in place.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RAB NEAR TERM...RAB SHORT TERM...MBS LONG TERM...MBS/WP AVIATION...RCS

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